Answer:
72 novels
Explanation:
A number of assumptions are involved regarding operating environment, utilization fraction, and probability of failure as a function of time. The precise meanings of the words "average", "supposed to last", "maximum", and "expect" are involved. The details are too arcane to go into here.
(450 hours)/(6 1/4 hours/novel)
= (450/(25/4)) novels
= (450*4/25) novels
= 72 novels